Adhesives and polymer sealants are now widely used to structurally join and seal parts which were previously welded. For example, in the automobile industry they are increasingly used to join and seal automobile bodies and body parts such as doors, hoods and trunks. Johnstone Pump Company of Troy, Mich. has been a leader in adapting large, commercially available six-axis welding robots to apply adhesives and sealants (hereinafter referred to together as adhesives) in precise, preprogrammed patterns to parts as they move down an assembly line. The adhesive must typically be applied in a fairly intricate, tightly controlled pattern, for which the six degrees of motion of these robot arms is well suited.
The adhesives are typically of extremely high viscosity, being nearly rigid at room temperature, and frequently require high operating pressures and thermal conditioning to achieve the desired flow. In a typical arrangement, a dispenser nozzle at the end of the robot arm is supplied by special hose with high pressure adhesive, and with fluids (water, air) needed for thermal conditioning of the adhesive and dispense valve operation.
In the prior art the thick, heavy, semi-rigid adhesive supply hose is coupled to a pressurized adhesive supply aft of the robot arm. The hose then runs along the length of the robot arm to the dispenser end of the arm to supply the nozzle. The wide range of motion of the robot arm requires the supply hose to be long enough to be extended, retracted, twisted, turned and dragged around as the robot arm moves the nozzle over the workpiece. This creates the simultaneous problems of 1) keeping the excess hose mounted reasonably close to the robot arm in the limited space provided on an assembly line, and 2) preventing the hose from being dragged or rubbed against the robot arm and dispenser assembly, which quickly wears out the strongest hoses unless they are provided with cumbersome, expensive protective sheathing.
Another problem encountered when dealing with substantial lengths of hose is the difficulty in pumping the high viscosity adhesive through the hose over long distances. A further problem encountered with hoses long enough to be manipulated through the full range of motion of the robot arm is the rigidity of the hose, particularly when "inflated" with the adhesive, which interferes with the ability of the hose to bend, turn and twist with the robot arm.
A related problem with prior robot arm adhesive dispensers is the location of the adhesive pressure regulator and flow monitor structure relative to the dispensing end of the robot arm. Normally the pressure regulator is mounted to the rear of the robot or on the floor, coupled to the dispenser nozzle through a length of the supply hose. This remote placement of the regulator structure prevents chafing and interference between the hose and dispenser components such as pressure regulators and flow monitors. However, the farther such flow-controlling devices are from the actual dispenser tip or nozzle, the less control the operator has over such critical dispensing factors as adhesive temperature, pressure, and volume.